The present invention relates generally to a hand-held scoring tool and method and, more particularly, to a tool and method for scoring an outer lead sheath of an electric cable conductor and removing the sheath after it is scored.
The tools according to the invention are usable on various electrical cable conductors, including those typically used as electricity transmission lines and lines for communicating control signals from one remote location to another, such as in downhole applications. More specifically, conductors used to transmit electricity to a downhole well tool are typically formed of three-conductor cable. An important use for these types of cables is for transmitting electricity to a submersible pump located inside the well bore through a power cable extending from an electrical source on the surface through the well bore and into the pump.
Insulation material is wrapped or extruded around each conductors, and an outer sheath of lead is typically extruded around the insulation material. The outer sheath is designed to isolate the conductor insulation from well fluids. The lead sheath has a ductility and flexibility which simplify the task of joining or splicing cables, and allows the cable to be wound on a reel. The lead sheath provides good fault carrying capabilities and acts as an effective barrier against moisture and chemicals, but does not impair the flexibility of the cable.
In the past, the lead sheath has been removed by cutting the lead in various places and then stripping it from the conductor. This crude technique has been unsatisfactory because it is time consuming and, if the lead is not cut carefully, the insulation can be cut and the conductor damaged. Thus, there is a need for a tool for removing the lead sheath in a way that is quick and easy to use in the field and does not damage the insulation or underlying conductor.
A tool and method have been developed in accordance with the invention, which are useful in removing a metallic or non-metallic outer layer or sheath, such as lead, from the outer surface of an electrical conductor. The tool and method involve scoring the outer surface of the sheath in such a way that the underlying insulation and conductor are not damaged, and then peeling the sheath from the insulated conductor.
The scoring tool includes a frame, preferably a C-shaped frame similar to that used in a pipe cutter, which straddles the electrical conductor and can be rotated about the cable for scoring the sheath. The tool has at least one scoring edge supported by the frame for engaging the outer surface of the insulated conductor when the frame straddles the conductor. The frame also includes a one or more rollers or other type of bearing surface, so that when the frame straddles the conductor, the conductor is located between the bearing surface and the scoring edge. The tool can be adjusted so that the scoring edge engages the conductor at a predetermined compressive force for creating a circumferential indentation in the outer surface of the sheath when the frame is rotated about the conductor.
The frame is also adapted to straddle the insulated conductor lengthwise, so that the frame can be moved along the length of the conductor for scoring the sheath longitudinally. This is done by forming a hole in the C-shaped frame through which the conductor can extend
The tool can also be provided with a second scoring edge disposed in parallel relation with the first scoring edge, either on one scoring wheel or on two separate scoring wheels. Preferably, the tool has a handle and a low friction surface for the bearing surface, which, along with the scoring wheel, facilitate movement of the frame relative to the conductor.
The present invention is also directed to a method for removing an outer layer or sheath (e.g., a lead sheath) from an insulated electrical conductor, which includes the steps of forming a pair of parallel score lines (or longitudinal indentations) lengthwise along the outer surface of the sheath, and lifting a free end of the sheath, located between the score lines, at the end of the conductor. The portion of the sheath located between the score lines is removed by progressively pulling that portion and separating it from the remainder of the sheath at the score lines. In a variation of the inventive method, the free end is lifted and rolled up along the conductor to peel off the portion of the sheath located between the score lines. The remainder of the sheath may then be pulled away from the conductor in a direction away from the removed portion.
The method may also include the step of forming at least one circumferentially extending score line around the sheath. This step may be performed prior to or after forming the pair of parallel score lines. In either case, the pair of longitudinal score lines end at the circumferential score line.